1. Field of the Invention
This invention is directed to nanoreinforced fibers, in general, and more particularly to methods of making nanoreinforced fiber tows or yarns for use in composite material applications.
2. Description of the Related Art
Carbon fibers are light weight materials that can exhibit high strength and high stiffness. Carbon fibers are typically produced by high-temperature pyrolysis of polyacrylonitrile (PAN), pitch, or rayon precursor. High heat treatment (above about 1000° C.) of polyacrylonitrile (PAN) based fibers results in essentially 100% carbon as well as a more oriented graphene microstructure and a significantly higher modulus. As the modulus increases, the fibers typically become more difficult to process resulting in increased costs due to heat treatment and subsequent processing (e.g., weaving). For example, at present, intermediate modulus (˜270 GPa) fiber in a woven fabric is approximately twice the cost of a standard modulus (˜220 GPa) fiber, but only exhibits about a 20% improvement in strength and stiffness.
In use, the carbon fibers may be processed or woven and then impregnated with resin to form a composite structure. Carbon fiber composites can exhibit a significantly higher strength to weight ratio in comparison to metals, resulting in a potential weight savings of up to about 50%. Carbon fiber composites also can have superior fatigue properties in comparison to metallic structures, and are corrosion resistant. With such advantageous structural properties, carbon fiber composites are suitable for use in various articles including aircraft and aircraft components.
Attempts have been made to overcome the processing challenges associated with carbon fiber formation while improving the carbon fiber's structural properties for use in various composite structures. These efforts include the use of carbon nanotube reinforcements to improve the strength and stiffness of various types of carbon fibers.
U.S. Pat. No. 7,153,452 references a mesophase pitch-based carbon fiber that includes carbon nanotube reinforcements in an amount ranging from about 0.01 percent to about 1.0 percent by weight. Other efforts have focused on structural improvements utilizing polyacrylonitrile (PAN)-based fibers. Such efforts include the use of an electrospinning process to align and disperse carbon nanotubes before introduction to polyacrylonitrile (PAN) precursors. The dispersion and alignment of the carbon nanotubes is believed by some to directly impact the carbon nanotubes' effectiveness as a reinforcement material. Titchenal, et al., “SWNT and MWNT Reinforced Carbon Nanocomposite Fibrils,” Drexel University, Society for the Advancement of Material and Process Engineering. In addition to electrospinning, mechanical and magnetic methods exist to align the carbon nanotubes before addition to the polyacrylonitrile (PAN) precursor.
There still exists a need for more efficient methods of enhancing or improving the structural properties of carbon and polyacrylonitrile (PAN)-based fibers. There also exists a need for using such fibers in composite structures.